Carbonization plays an important role in preparing a carbon/carbon (C/C) composite. Not only the properties, the economical efficacy of a C/C composite is critically dependent on a careful control of its carbonization process due to the fact that carbonization is one of the most time and energy-consuming steps in the entire fabrication process of C/C composites, especially for those densified by liquid phases.
Logically the simplest way to reduce the manufacturing cost of C/C composites is to increase the carbonization rate, which is usually very low. However, carbonization is primarily a process of pyrolysis of hydrocarbons of a carbon precursor. The pyrolysis of hydrocarbons generally involves such processes as the cleavage of C—H and C—C bonds to form reactive free radicals, molecular rearrangement, thermal polymerization, aromatic condensation and elimination of side chains (e.g., H2) [Lewis, 1982; Lau{hacek over (s)}ević and Marinković, 1986]12, 9. To minimize such adverse effects as shrinkage, cracking and thermal stresses that may build up during carbonization, low carbonization/heating rates (<20° C./min) are usually required [Olsen et al., 1997; Sastri et al, 1999, Ko and Chen, 1991; Roy, 1993; Chang et al., 1994; Gupta and Harrison, 1994; Prevorsek and Li, 1996; Lewis and Howard, 1997; Hager et al., 2000; Murdie et al., 2000]18, 21, 8, 20, 1, 4, 19, 11, 6, 15.
Ko and Chen [Ko and Chen, 1991]8 studied the pyrolysis of a plane-woven PAN (polyacrylonitrile)-based carbon fabric/phenolic resin composite, and observed that in their heating rate range (0.1-5° C./min), the heating rates below 3° C./min had no effect on the carbon yield of the composite carbonized to 1000° C. Roy [Roy, 1993]20 found that in the heating rate range of 0.03-0.8° C./min, the interlaminar tensile strength of their 8H satin woven PAN-based UHM carbon fabric/phenolic resin composite was not affected by the heating rate. Chang et al. [Chang et al., 1994]1 revealed that in the range of 0.5-3° C./min, the density and flexural strength of their plane-woven PAN-based carbon fabric/phenolic resin composite declined by 0.7% and 6.6% respectively, when a higher heating rate was used. The weight loss and flexural modulus were not affected. In their research on an 8H satin woven PAN-based carbon fabric/phenolic resin composite carbonized to 1000° C. at a heating rate of 2-7° C./min, Nam and Seferis [Nam and Seferis, 1992]17 discovered that a higher heating rate and a larger thickness of the composite resulted in a larger temperature gradient within the composite. This temperature gradient could result in a non-uniform carbonization, creating internal stresses through the laminates, which in turn, might lead to localized delamination and/or other damages to the char structure of the matrix.